This invention relates to display devices, and more particularly, to monolithic light emitting semiconductor display having a lens structure integrated in the monocrystalline structure. Displays formed by light emitting semiconductor devices are frequently used because they afford reliability, ruggedness, and economy. In such art there is a pressing need to increase reliability and ruggedness, and to reduce cost by simplifying fabrication, so as to make use of such displays more practical.
One of the most recent advancements in the art of such displays consists of constructing a light emitting display array of two separate sections. The first section is substrate or base in which are mounted in a precise pattern a plurality or separately manufactured light emitting semiconductor devices, i.e. light emitting diodes (LED's). The second section consists of a glass plate having precisely etched or otherwise formed in its top surface a plurality of parabolically-shaped reflecting recesses. The two parts are secured together in a suitable manner with each reflecting recess carefully aligned with its respective LED in the substrate. Such a display array has advantages in that it is extremely reliable, rugged in construction, and provides a very flat display, i.e., a low ratio of display volume to area.
There is, however, a significant disadvantage in the above described display array because of the relatively high manufacturing cost. This disadvantage arises primarily because of the precision required in the etching of the reflecting surfaces, and in locating the LED's on the substrate, and in addition the precision that is required in mounting the reflector plate to the base so that each reflecting surface is very accurately aligned with its respective LED. This amounts to a large number of manufacturing steps and processes.
There is another prior art light emitting display using semiconductor devices together with integral lenses illustrated in U.S. Pat. No. 3,631,360 issued Dec. 28, 1971. This patented structure utilizes an integral Fresnel lens (zone plate) to focus the emitted light rays. The Fresnel lens comprises a planar arrangement of spaced opaque regions separated by transparent regions. Unfortunately, the use of opaque regions in the zone plate materially reduces the available light from the LED's which inherently produce barely enough light to be satisfactory for most applications.
The method of this invention greatly reduces the cost of fabricating light emitting display devices, maximizes the amount of useful light available from the semiconductors used in these displays, and greatly improves reliability.